Thursday 19 November 2015

Cycling rodents

Yesterday I was focussing a blobby eye on evidence for a 26 my periodicity in global mass extinctions.  We can't blame coal-fired power-stations or teak furniture for those events.  Some of the most interesting aspects of biology focus on ups and downs and today we're looking at cycles that are 10 million times more zippy than the wobbles of Nemesis.
When I was in graduate school in Boston I was given a desk in the Tamarin vole-lab, where I learned a lot that wasn't directly relevant to my thesis; like how to eat ice-cream with a spatula. The existence of the vole Microtus pennsylvanicus lab was predicated on the fact that they went through regular boom&bust population cycles of about 3 years.  My office mates used to take blood and other data from these small mammals to see if they could get a genetic handle on the peculiar phenomenon of huge fluctuations in population density.  At the same time on the other side of the pond, Nils Stenseth, a very smart population ecologist was doing similar work on the Norwegian Lemming Lemmus lemmus which showed similar bizarre see-saws in numbers from zero to tons per hectare to zero again on a 3-4 year cycle. No, they don't fling themselves off Norwegian cliffs in a vain attempt to go watch Rangers play soccer at Ibrox Park, Glasgow. Stenseth had studied theoretical evolutionary biology under John Maynard Smith and had a track record for a) interesting ideas and b) an all-embracing view of systems which was not too much fettered by the reductionist norms of scientific practice: he thunk BIG.  Here, as a grand old man of Norwegian science, he is talking about best practice for a rational future in science and politics. Biology is complex, let's not make things so simple that they become simple-minded.

Well it turns out that Norwegian lemmings have stopped cycling in the 30+ years since I was at all up to date with that literature. Apparently its mainly because of the wrong sort of snow.  Stenseth and his team corralled a huge amount of disparate data, not only on weather and climate, but also predator densities and food availability and other parameters and then dumped the whole mess into a computer to sort through looking for patterns that preceded or were coincident with the lemming cycles. Dense population seemed to follow after Winters with the right sort of light, cold, dusty snow under which the lemmings could run about shagging each other senseless and bringing a litter of baby lemmings into the world three weeks later.  No snow or a sludgey Gulf Stream snow and any active lemmings get scooped up by foxes, both Arctic Alopex Vulpes lagopus and Red Vulpes vulpes and eaten. T'buggers have changed the name of the Arctic fox from Alopex: is nothing sacred stable in biological nomenclature? That's a major change, presumably climate-change driven, that affects the distribution of all the other plants and animals in the ecosystem.  Most obviously among the predators and their prey. That's evolution happening before our eyes. It's wonderful and rare to have that happen in a single human lifetime. Although evolution can be seen to happen in a single mm of the fossil record, that's still hundreds or thousands of years of gene frequency change.

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